1. Field of the Invention
The present invention relates to building construction, and more specifically, to apparatus for anchoring walls to foundations and lower floors.
2. Background
Strong winds and earthquakes subject walls and others elements of a building to tremendous forces. If these forces are not distributed to the proper elements or structures capable of withstanding such force, the building may be tom apart. Foundations are often the strongest element of a building. Securely tying the walls of a building to the foundation greatly improves structural performance during periods of strong wind or earthquake. Securement promotes single body motion and limits whiplash amplification that often results in structural failure.
Under extreme conditions, a building may be violently loaded or shaken back and forth in a lateral (side to side) direction. If a shear wall is tightly restrained at its base, loads may be smoothly transferred to the foundation. The loads may then be resolved in the foundation, where they appear as tension and compression forces.
Buildings are often composed of long walls, (walls with a length greater than the height) and short walls (walls that have a length shorter than the height). The tendency for a wall to lift vertically off a foundation is inversely proportional to the length of the wall. Tall narrow shear walls, which may be found in nearly all homes, act as lever arms and may magnify an imposed load. In certain instances, the actual load on the securement system may be magnified to several times the originally imposed load.
Wall securement may prevent lateral and vertical motion between the walls and the foundation. Additionally, it may be necessary to support the wall against forces that would tend to distort the wall's general rectangular shape. Building codes often require external and load bearing walls to be shear resistant by providing a plywood plane to support shear forces that may be imposed on the wall. Many times, building codes also require lateral and vertical securement of a wall to the foundation. Lateral and vertical securement may be accomplished by employing hold-downs, also referred to as tie-downs.
Typically, hold-downs are attached eccentrically, spaced from the neutral axis, on a selected number of support members (e.g. posts, beams, or studs) which make up the wall of building. Eccentric attachment introduces a moment in the support member that greatly reduces the tensile capacity thereof. Eccentric attachment may also cause the support member to deflect excessively. The tensile force caused by tightening the hold-down may cause the support member to bow. Bowing tends to promote column buckling and reduces the effectiveness of the support member to provide sufficient structural support.
Moreover, hold-downs are difficult to install and expensive to fabricate. Accordingly, a need exists for a balanced hold-down that may be easily installed. It would be a further advancement to provide a balanced hold-down that may be produced in greater quantities with greater speed and less expense.